1. Technical Field
The present invention relates to a substrate for electro-optical devices, an electro-optical device provided with the substrate for electro-optical devices, and an electronic apparatus provided with the electro-optical device.
2. Related Art
As an example of this type of a substrate for electro-optical devices, for example, there is an active matrix substrate which is used in an electro-optical device such as an electrophoretic display device of an active matrix driving method, and is provided with a pixel electrode and scanning lines, data lines, and a thin film transistor (TFT) acting as pixel switching elements for performing selective driving of the pixel electrode, on the substrate. The above constituent elements are formed in a laminated structure on the substrate. Each of the constituent elements is arranged so that each layer is separated and isolated by interlayer insulating films, and are appropriately electrically connected via contact holes (also called “through holes”) formed in the interlayer insulating films.
Also, the substrate used in this type of electro-optical device is changing from glass substrates which have low flexibility (in other words, rigid) used in the past to plastic substrates which are light and have superior flexibility. As a result, there is demand for a substrate for electro-optical devices provided with a TFT corresponding to the flexibility of the substrate.
For example, in JP-A-2009-38337, a technology is disclosed for manufacturing organic thin film transistors by applying a material in a limited manner to a region for film deposition using a printing method. According to such a technology, an etching process for forming contact holes can be reduced.
However, in JP-A-2009-38337 described above, as a gate insulating film is formed over the entire surface of the substrate, problems such as those below occur. A first problem is that the substrate is bent by stress in a film when using a plastic substrate due to the gate insulating film being formed on the entire surface of the substrate. A second problem is that, as the gate insulating film is present over the entire surface of the substrate, a process is necessary for opening contact holes in the gate insulating film for connecting the gate electrode and an external electrode or for forming a circuit such as a protection diode on the substrate, and thus, the manufacturing process becomes complicated. A third problem is that, as the gate insulating film is formed over the entire surface of the substrate, this goes against demands for saving resources and lower costs.
It is known that if there is large stress in the substrate, not only is the shape of a final product deformed but transportation is not possible when there is bending of the substrate during processing, and in extreme cases, the substrate becomes a roll shape and treatment in later processes cannot be performed. Furthermore, it is also known that as stress increases as the film forming is repeated, the problem increases in the later processes. These problems become further pronounced when using the plastic substrate as described above.